A method and an apparatus for damping a sonic signal

ABSTRACT

A method for limiting the sound volume in an earphone, a headset ( 8 ), or the like, to a maximum permitted level, entails that an input signal ( 2 ) is sensed by a processor ( 4 ) and damped by a damper ( 6 ) if it is excessively high. Thereafter, the signal ( 7 ) is transmitted to the earphone, the headset ( 8 ), or the like. The processor ( 4 ) switches between an active mode and a rest mode. An apparatus for limiting the sound volume according to the method includes a microprocessor ( 4 ) and a damper ( 6 ).

TECHNICAL FIELD

The present invention relates to a method for limiting the sound volumein an earphone, a headset, or the like, to a maximum permitted level,comprising the steps that an input signal to the earphone, the headsetetc., is sensed by a processor, and that, at an excessively high levelof the input signal, the signal is damped by a damper before beingtransmitted further to the earphone, the headset, etc.

The present invention also relates to an apparatus for limiting thesound volume in an earphone, a headset, or the like, applying the abovemethod.

BACKGROUND ART

The use of portable music playing devices, such as for example CD-andMP3 players and the like is becoming increasingly common. As a result,it has been found that the risk of hearing injury increases, since it isfar too easy to increase the sound volume to a level which risksinjuring the hearing of the user. Not least, this is the case when thesound volume is increased so as overcome ambient noise, for exampletraffic noise.

In order to reduce disturbances from ambient noise or sound, certainearphones are formed as sealing plugs, which exclude airborne sound fromthe ambient environment, but where the sound from the music player isallowed passage. The drawback in this feature is that the effect fromthe sound signal is concentrated to the eardrum, since the sonic wavesfrom the earphone cannot propagate outwards, in a direction away fromthe ear of the user. With this type of earphone, the risk of injury tothe hearing is particularly manifest.

For some time, increasingly stringent requirements have begun to beplaced on a limitation of sound levels, in order to avoid the occurrenceof sound levels that are harmful to the auditory system. Those attemptsthat have been made have generally entailed providing the music playerswith some type of software which limits the outgoing sonic signal fromthe player.

In certain cases, this solution could function well, but unfortunatelysuffers from certain drawbacks. Often, the software can be disengaged bythe user if the user is not satisfied with the sonic signal obtained.Such users are often children or youngsters who are well aware of howthe music players can be operated, but do not realise the consequencesof exposing themselves to excessively high sound levels. Most generally,their parents have no control over how the software of the music playeris manipulated.

Another drawback is that one and the same output signal from a musicplayer can give totally different sound volumes in the ears of the user,depending on the type of earphone employed. Thus, if the player is usedwith those earphones or headsets which are supplied as standard onpurchase, the sound levels may be completely safe and acceptable.However, if the earphone or headset is replaced, either because it isexperienced as being insufficient by the user or because of some type ofdefect and must be replaced, the results can be totally different. Thesonic signal to which the listener's ears is exposed can at once amountto unsuitable or quite simply harmful levels. Thus, it is suitable ifthe damping feature is adapted to the earphone or headset and isconnected to it.

Certain types of digital signal processing have been tried where thesignal passes through a processor before reaching the earphone. Onedrawback is that power consumption is relatively high, which implieseither that the batteries that are used in the player quickly needrecharging or replacing, or that the earphones must be provided withseparate batteries. Another drawback is that the sound quality isaffected, which is of major importance in listening to music. However,there are occasions when sound quality is of lesser importance, forexample when the earphones are principally used to transmit the spokenword and similar short messages, as is, for instance, the case incertain types of hearing protection.

PROBLEM STRUCTURE

Thus, it is the object of the present invention to maximise the soundquality obtained in an earphone, a headset, or the like, at the sametime as power consumption is minimised and a reliable damping to a safesound level is obtained.

SOLUTION

The objects forming the basis of the present invention will be attainedregarding the method if this is characterised in that the processorswitches between a state where it is in active mode and a state where itis in a passive or rest mode.

Concerning the apparatus, the objects of the present invention will beattained if the apparatus is characterised in that it comprises amicroprocessor and a damper.

Further advantages will be attained if the present invention is moreovercharacterised by any one or more of the characterising features as setforth in appended Claims 2 to 8 and 10 to 12, respectively.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will now be described in greater detailhereinbelow, with reference to the accompanying Drawings. In theaccompanying Drawings:

FIG. 1 is a block diagram of the apparatus according to the presentinvention in broad outline;

FIG. 2 is a block diagram of the microprocessor included in theapparatus;

FIG. 3 is a block diagram of the method according to the presentinvention in broad outline; and

FIG. 4 is a block diagram of the active mode included in the method.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the Drawings, FIG. 1 shows in broad outline the apparatusaccording to the invention for damping a sonic signal 2 from a musicplayer 1 before it reaches the listener's ears.

The music player 1, which may be a CD player, an MP3 player or someother type of music player, emits a sonic signal 2 which functions as aninput signal to the damping device according to the invention, thisdamping device being physically connected to earphones 8, and cannot bepermanently disconnected therefrom. When the input signal 2 exceeds apredetermined level, it will be damped by a damper 6 before beingtransmitted further to the earphones 8 in the form of an output signal 7from the apparatus. The damper 6 is controlled by means of a controlsignal 5 which derives from a microprocessor 4. The microprocessor 4senses the input signal 2 with the aid of a sampling signal 3, whichconstitutes an extremely small part of the input signal 2, but which isnevertheless sufficient to determine the sound level of the input signal2. The sensing takes place in the order of magnitude of 100 times/s.,which implies that the microprocessor 4 is not utilised to its fullcapacity for the greater part of the time.

The damper 6 is a per se previously known component, but it requires acontrol signal 5 produced in a suitable manner to be able to emit anoutput signal 7 which does not exceed the maximum desired sound level.

The microprocessor 4 is similarly a standard component with low energyconsumption, but if it is disposed according to the invention and drivenaccording to the invention together with the damper 6, the result willbe an energy miser sound damping with maintained sound quality. It iseven possible to expect that the apparatus requires such little energythat it can be driven using one and the same battery throughout itsentire service life.

For this to be possible to achieve, the microprocessor 4 and the damper6 are, in the preferred embodiment, connected in parallel to one anotherso that the sonic signal 2 which is to be damped is not led straightthrough the microprocessor 4, but is led directly to the damper 6 whichis controlled digitally by the microprocessor 4 based on a sampling 3,i.e. a sensing of the input signal 2.

FIG. 2 shows the microprocessor 4 schematically with several details.The microprocessor 4 is a standard component, implying that it displaysa number of different functions, of which not all are employed in thepractical application of the present invention. Those functions that arenot utilised have been omitted from FIG. 2. The microprocessor 4 has anexternal low speed clock 9 which is used in the sampling 3 of the inputsignal 2. In the present invention, it has in practice proved tofunction with a frequency of 400 kHz, the current consumption being0.003 mA.

An internal high speed clock 10 is used on calculations and the like inthe microprocessor 4. Its frequency is, in practical applications, about8 MHz, which implies that it is not possible to use this clock 10 onsampling 3, since the frequency is far too high for sampling a sonicsignal.

An A/D converter 11 is employed for reading the input signal 2 from themusic player 1, i.e. on the sampling 3 of the input signal 2. It is thusthe A/D converter 11 that directly senses the analog input signal 2 andconverts the sensed signal to a digital value, while the external lowspeed clock 9 determines at which rate this is to take place.

In the core 12 of the microprocessor those calculations take place thatare necessary on processing of the sampling 3 of the input signal 2, forgenerating the control signal 5 to the damper 6. The calculation takesplace at the speed of the internal high speed clock 10.

Further, there is at least one wake-up unit 13 which, on the one hand,can realise a periodic waking-up from a rest or passive mode of themicroprocessor 4 roughly twice/s so that a new sampling series 3 can betaken up. The wake-up unit or units 13 can also realise a waking-up ofthe microprocessor 4 on an external impulse, e.g. a button push. Thistakes place when the microprocessor 4 has entered into a rest mode aftera lengthy period of silence, i.e. the absence of an input signal 2.

FIG. 3 shows a block diagram of the broad features in the method forsound damping according to the present invention.

In broad outlines, there are four different steps in the method.Initially, the method undergoes a mobilisation or start-up stage 14where all hardware is installed and the software initiated, so that themethod can switch between different modes throughout the entireoperational life of the apparatus. Thus, the mobilisation stage 14 needonly be completed once during the operational life of the product.

When the initiation has been completed and the different clocks 9 and 10have been started, the process can enter into the next stage, the activemode 15. In the active mode 15, a sampling 3 is undertaken at regularintervals in time, and from the sampling 3 a mean sound level iscalculated so that damping can be put into effect. Now and then, a checkis made to ensure whether the battery voltage is sufficient in thatbattery which drives all of the hardware. In order to save the batteryas much as possible, and thereby prolong its service life, operation isnot continuous, but the process enters into temporary, energy-savingrest modes, on the one hand between the series of samplings and the meanvalue calculations and, on the other hand, when the incoming inputsignal 2 is so low that no damping thereof is necessary.

A more lengthy rest mode 16 is attained after the sampling 3 has notshown any input signal during the last 2-4 hours, i.e. in the event ofsilence when the music player 1 is not in use. In order for the processto revert to the active mode 15 from the rest mode 16 and the clocks 9,10 once again be started, an external signal is required in the form ofa button push. Essentially, it is the detection of the button pushoperation which is the only function remaining during the rest mode 16.

As was mentioned above, the battery voltage is checked at regularintervals, battery interval t_(b), in the active mode 15. When thebattery is considered to be dead, in that an excessively low batteryvoltage has been recorded on a predetermined number of occasions, theprocess moves into a state of permanent locking 17, from which it cannotreturn, and the damping device must then be considered as consumed.

FIG. 4 shows a block diagram of the active mode 15 with additionaldetails therein. In sequence, in the active mode 15, there is first asampling of the input signal 2, which is typically divided in twochannels, one for the left and one for the right earplug, respectively.The sampling takes place alternatingly between these two channels. Thesampling is repeated 64 times in the preferred embodiment and takesplace at the speed of the external low speed clock 9.

Thereafter, a data processing of the sampled data takes place. If any ofthe right or left channels shows a zero value, data is copied from theother channel, so that two complete channels are obtained. A mean valueof the sampled data is calculated, and since the sampling takes placeduring a limited time, this is a short time mean value. In the nextstage, a comparison is made between the mean value and the maximumpermitted value, and if the mean value exceeds the maximum permittedvalue, a control signal 5 is transmitted to the damper 6 to immediatelyincrease the damping, whereafter the processor 4 can go into anenergy-saving mode until the next sampling. If on the other hand themean value is less than the permitted maximum value, no immediateincrease is needed, but the damping is compared with a damping targetvalue and can be changed to a long-term mean value, which is based onthe results of a plurality of samplings 3, at a fixed change speed. Thelong-term mean value is calculated with the time interval t_(tm),long-term interval.

Every battery interval, roughly once an hour, a check is made of thebattery voltage, as mentioned above. This part of the process entailsthat the battery voltage is measured and compared with a least permittedvalue. If the value is found to be exceedingly low, this fact isregistered and when an excessively low value of the battery voltage isregistered on a number of occasions, so that it is absolutely certainthat the battery is genuinely about to die, the process enters into themode of permanent locking 17. From this mode 17, the process cannotreturn and the damping device and its associated earphone or headset isthereby consumed.

DESCRIPTION OF ALTERNATIVE EMBODIMENTS

Conceivably, one or more of the features in the above-describedembodiment of the present invention can be modified. For example, it isconceivable that the locking when the battery is dead is not madepermanent, but that this can be remedied by a battery replacement, whichimplies that the process then restarts from its initial stage 14.

Another method of modifying the present invention is that the speeds ofthe clocks 9 and 10, for example on the calculation or the sampling, canbe adjusted. However, it must be ensured that, after the adjustment, theapparatus is still within that range which functions in this particularapplication. For example, the sampling frequency may not be higher thanthat it is still possible to sample sound frequencies within the audiblerange. Other examples of variations are that the time between two checksof the battery voltage is varied, that the time of absence of inputsignal before the lengthy rest mode 16 is attained is changed and thatthe time interval between different sampling series is varied.

The present invention may be modified further without departing from thescope of the appended Claims.

1. A method for limiting a sound volume in an earphone or a headset to amaximum permitted level, comprising the steps of: sensing by a processoran input signal to the earphone or the headset, and when the inputsignal exceeds a predetermined level, damping the input signal by adamper before transmitting it further to the earphone or the headset,wherein the processor switches between a state where it is in an activemode and a state where it is in a rest mode.
 2. The method as claimed inclaim 1, further comprising an initial mobilization step.
 3. The methodas claimed in claim 1 further comprising a permanent locking step. 4.The method as claimed in claim 1, wherein after a lengthy period ofabsence of an input signal, the processor switches to its rest mode fromthe active mode.
 5. The method as claimed in claim 1, wherein theprocessor switches to its active mode from the rest mode in response toan external signal.
 6. The method as claimed in claim 1, wherein thebattery voltage is measured periodically.
 7. The method as claimed inclaim 1, wherein if the incoming input signal is so low that no dampingis necessary, the processor switches to an energy saving mode.
 8. Themethod as claimed in claim 1, wherein the sensing takes place in theactive mode of the processor, the input signal being periodicallysampled, a mean value being calculated, a comparison being made with amaximum permitted level, and a correct damping being set.
 9. Anapparatus for limiting a sound volume in an earphone, or a headset, theapparatus comprising a microprocessor capable of sensing an input signalto the earphone or the headset and switching between a state where it isin an active mode and a state where it is in a rest mode, and a dampercapable of damping the input signal before transmitting it further tothe earphone or the headset when the input signal exceeds apredetermined level.
 10. The apparatus as claimed in claim 9, whereinthe microprocessor is connected in parallel with the damper.
 11. Theapparatus as claimed in claim 9 wherein the microprocessor includes ahigh speed clock for processing sensed data from the input signal. 12.The apparatus as claimed in claim 9, wherein an external clock isdisposed outside the microprocessor for controlling the speed forsensing of data from the input signal.
 13. The apparatus as claimed inclaim 9, wherein the damper is controlled by the microprocessor based onsensing of the input signal.
 14. The apparatus as claimed in claim 13,wherein the microprocessor generates a control signal to the damper. 15.The apparatus as claimed in claim 9, further comprising a wake-up unitthat realizes microprocessor waking-up from a rest mode.
 16. The methodas claimed in claim 6, wherein if an excessively low battery voltage hasbeen recorded on a predetermined number of occasions, the process entersa permanent locking step.
 17. The method as claimed in claim 1, whereinsensing the input signal comprises sampling the input signal.
 18. Themethod as claimed in claim 17, wherein the input signal is divided intwo channels and the sampling takes place alternatingly between thesetwo channels.